A method for coating washers for locking and coated washer for locking

1. Background

1.1 Technical field

The present invention relates to a method for coating washers for locking according to the introductory part of the attached claim 1.

The invention also relates to a coated washer according to the introductory part of the attached claim 11.

1.2 Prior art

Washers for locking, eg for bolt securing purposes, having a plate-like shape and on preferably one side a pattern of radially extending teeth and on the other side a pattern of preferably radially extending cams and comprising a central hole for a bolt, a screw or the like fastening element, are previously known. A pair of washers are intended to be applied together, the cam patterns facing each other and tooth patterns being intended to engage a bolt head, a nut or the like and a support or the like, respectively.

In order to obtain an efficient engagement and to resist the considerable force applied to the fastening arrangement the washers are made of a hardenable steel and hardened.

Furthermore, in order to, among other things, resist corrosion, the washers are provided with a coating of zinc, which is applied electro lyrically.

A serious problem related to this prior art technique is that during the electrolytic application of the zinc coating, hydrogen is developed, the hydrogen on an atomic

scale being solved in the washer steel and causing so-called hydrogen embrittleness, the embrittlement being due to the fact that the hydrogen atoms solved locks dislocations in the steel and, thus, reduces the steel ductility.

To substantially reduce or totally eliminate the hydrogen embrittleness, the washers, which have been hardened and, normally, slightly tempered, are heat treated at about 200 ⁰ C for about 48 hours to drive the solved hydrogen out of the steel. This is of course an expensive and time consuming operation which, however, is necessary. Further, said heat treatment tends to add tempering to the hardened steel so that the intended hardness will not be maintained but considerably decreased.

Furthermore, today there is a need for harder washers to be combined with harder bolts and pin bolts for gripping by the washer pattern of teeth. However, such harder washers are obtained by increasing the carbon content to the steel which makes the washers even more sensitive to hydrogen embrittlement and additional tempering during said heat treatment.

The object of the present invention is to provide a method and a washer which offers a solution to the problems described above.

2. Summary of the invention

The above identified object is obtained by a method and a washer according to the attached independent claims 1 and 11 , respectively. Further advantages are obtained by means of what is specified in the respective dependent claims.

3. Brief description of the drawings

A better understanding of the present invention will be had upon the reference to the following detailed description when read in conjunction with the accompanying drawings, wherein like reference characters refer to like parts throughtout the several views, and in which

- Fig. 1 shows in a schematic view a prior art bolt securing system employing a pair of washers and

- Fig. 2 schematically shows, in the form of a block diagram, a first embodiment of a method according to the invention,

4. Detailed description of preferred embodiments

In Fig. 1 , 1 designates locking washers of the kind intended to be manufactured by the method according to the invention and to be arranged according to the invention.

The washers are for locking purposes, eg for securing a bolt 2, each washer having a plate-like shape and on one side a pattern 3 of teeth and on the other side a pattern 3' of cams and comprises a central hole, not shown, for a fastening element 2, such as a bolt, a screw or the corresponding, the washers being intended to be applied in a pair, the cam pattern sides facing each other, and provide a self-locking action when the pitch α of the cams exceeds the pitch β of the threads of the fastening element as shown in the example of Fig. 1.

According to the embodiment of Fig. 2 of the method according to the invention, washers 1 , which have been previously hardened by heating to an austenitizing temperature and subsequent quenching, are, in some cases after certain tempering, supplied to a pre-treatment step 4 as indicated by the arrow 5. The pre-treatment may include washing and blasting and depends on the surface status of the hardened

washers. In some cases it might be desirable to temper the hardened washers to a certain extent before coating, preferably to a quite limited extent such as to an extent decreasing the steel hardness by about 5-15 %, preferably by less than about 10 %. Many steels, such as low alloy boron steels are quite ductile as hardened and do not need any tempering for the present purpose.

After the pre-treatment a basic coating application step 6 follows, preferably in a centrifugal device 6, to which the washers 1 as well as coating in liquid form are transferred as indicated by arrows 7 and 8, respectively. In a curing step, generally designated by 9, the applied basic coating of the washers is cured, the liquid components of the basic coating being removed by heating. The curing step 9 may, according to a preferred embodiment, include a pre -heating step 9' and a main curing step 9" followed by a cooling step 9'". After having passed the curing step 9 the washers are covered by a metallic basic coating. According to embodiments sometimes preferred, the washers having a first basic coating are recirculated to the basic coating application step 6, as indicated by the arrow 10, and further to the curing step 9 for application of another layer of basic coating.

Further, according to preferred embodiments, a post sealing top coat is applied over the basic coating of the washers, which are for this purpose transferred to a top coat application line as indicated by the arrow 11. According to preferred embodiments this line includes a top coat application step 12, preferably in the form of a centrifugal device 12', into which the washers as well as top coat in liquid form are transferred as indicated by the arrows 11 and 13, respectively. In a curing step, generally designated by 14, the applied top coat is cured, the liquid components of the top coat being removed by heating. Also this curing step may include a preheating step 14' and a main curing step 14" as well as a cooling step 14'".

In an alternative embodiment sometimes preferred the top coating application step is performed in the same application step, preferably in the form of a centrifugal device, as the basic coating application step, preferably in the form of a centrifugal device.

This embodiment is indicated in fig. 2 by means of the arrows 11 ' and 13' leading to the step 6, 12" for the washers and the top coat, respectively, the curing step 9 preferably also being used for curing the applied top coat according to this alternative embodiment the process parameters of the curing step 9, however, when applicable, being adapted for this alternative curing step. A separate curing step 14 for the top coat may however be imagined also in this embodiment, as indicated by the arrow 15.

The coating step/-s of the method according to the present invention is/are performed non-electro lytically and under conditions such that tempering of the hardened washers is prevented or substantially prevented.

Thus, typically, the curing step 9 for the basic coating comprises pre-heating for about 10 minutes at about 60-120 ⁰ C, preferably about 8O ⁰ C, and main curing for less than 60 minutes, preferably less than 20 minutes, such as for about 15 minutes, at about 200 ⁰ C, preferably at about 190-230 ⁰ C.

Further, typically, the curing step 14 for the top coat comprises pre-heating for about 10 minutes below 200 ⁰ C and main curing for less than about 20 minutes, preferably for about 10 minutes, at about 200 ⁰ C, preferably at about 190-210 ⁰ C.

The basic coating as cured comprises a metallic layer comprising zinc flakes, and, more specifically, a metallic layer comprising a mixture of zinc flakes and aluminium flakes, the basic coating providing anti-corrosion properties for the washers. Typically, the metallic layer comprises about 74 % zinc and about 8 % aluminium by weight.

The post sealing top coat provides a sealing for the basic coating and makes sure that corrosion of the washer steel does not occur via porosities in the basic coating. Preferred is a top coat comprising dilithiumoxide.

According to preferred embodiments the basic coating is of the kind available on the market under the name DELTA PROTEKT™ KL 100 and the top coat is of the kind available on the market under the name DELTA PROTEKT™ VH 300, preferably of the kind VH 302 GZ or VH 301 GZ.

According to a specific embodiment the DELTA PROTECT™ KL 100 basic coating comprises substantially about

74,27 % zinc, 8,07 % aluminium,

14,3 % titaniumdioxide and 3,5 % silicondioxide.

Further, according to a specific embodiment the DELTA PROTECT™ VH 300 (VH 302 GZ or VH 301 GZ) top coat comprises substantially about

61 % silica amorphous, 30,3 % dilithiumoxide, The rest not to be declared.

Typically, the basic coating layer has a thickness of about 6-20 μm, preferably about 10 μm, and the top coat layer a thickness of about 1-3 μm.

According to preferred embodiments the hardness of the washer steel as coated is over 500 HV, preferably about 500-560 HV.

As washer steels a large number of different steels may be chosen.

According to preferred embodiments low-alloy boron steels are used, these steels substantially comprising

0,25-0,30 % carbon 0,20-0,35 % silicon

1,00-1,30 % manganese

0,030 % phosphorus

0,010 % sulphur

0,20-0,60 % chromium and 0,0015-0,0050 % boron, the balance iron and normal impurities.

According to other preferred embodiments the washer steel carbon content is higher than 0,3 % by weight, preferably 0,3-0,5 % by weight, an example being a low- alloy boron steel according to European standard 30 MnCr B5, substantially comprising

0,3-0,36 % carbon

< 0,4 % silicon 1,2-1,5 % manganese

< 0,035 % phosphorus

< 0,040 % sulphur 0,3-0,6 % chromium 0,0008-0,005 % boron, the balance iron and normal impurities.

Example 1

Washers of the type NLlO made from a boron steel of the type Boloc 04, having a composition as given for the preferred 0,25-0,30 % carbon low-alloy boron steels above, were heated to austenitizing temperature and subsequently quenched in water this producing a hardness of 581 HV. Subsequent tempering, preferably on-line in a band furnace, in 30 minutes at 200 ⁰ C produced a hardness of 529 HV, ie a hardness drop of about 9 %.

The washers thus treated were then given a DELTA two layer basic coating and a one layer top coat as described above, each layer being heated at 200°C for about 15 minutes, the hardness being about 513 HV after the coating treatment.

The method and the washer according to the invention should to a sufficient extent have been made clear from the description given above.

Thus, washers hardened to the desired hardness are coated non-electrolytically, the coating procedure involving heating to a temperature such that tempering of the hardened washers is avoided or substantially avoided. In addition to the maintained hardness the method provides an improved productivity.

Above the invention has been described in association with preferred embodiments. Of course further embodiments as well as minor additions and amendments may be imagined without departing from the basic inventive idea.

Application of the basic coating and the top coat may be performed as described above, the washers, after having been dipped in the liquid coating/coat, being processed in a centrifugal device for removal of access liquid. Other methods than this so-called dip-spin may be used, such as dip-drain (removal by draining without centrifugal device) or spraying.

Heating for pre -heating and curing may be performed in a suitable furnace, such as a gas-fired or electrical furnace.

The method according to the invention is also applicable for a nut to be used together with a pair of washers, each one being provided with a pattern of teeth and a pattern of cams, as well as for a nut provided with a pattern of teeth to be used together with a washer according to the invention.

Thus, the invention should not be considered limited to the embodiments shown but may be varied within the scope of the accompanying claims.