Coating of lead spheres
09-25-2006, 03:40 PM,
#1
Question  Coating of lead spheres
We manufacture equipment for the nuclear industry, one item being a Tong Ball which is a lead sphere through which passes a tong grab, the ball is mounted in a lead shield housing allowing the operator to gimble the tong anywhere within the containment. At present the lead ball is manufactured and spray coated with chrome to reduce wear in the gimble housing, this is prone to cracking and the operation has become very expensive. Is there another coating such as a form of ceramic or teflon which can be sprayed on a spherical lead surface with an even coat to reduce the final machining and also give the required durability.
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09-25-2006, 11:47 PM,
#2
RE: Coating of lead spheres
Hi Headland

Welcome to the Surface Engineering Forum.

A few questions:

Question Is the bearing surface in the housing lead?

Question Is it lubricated or run dry?

Question What would you estimate the maximum possible temperature the lead ball could withstand, before danger of creeping out of shape?

Question Do you mean electroplated hard chromium instead of spray coated chrome?

Question Do you think chrome coating is failing due lack of support from lead substrate?
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09-26-2006, 11:17 AM,
#3
RE: Coating of lead spheres
Gordon Wrote:Hi Headland

Welcome to the Surface Engineering Forum.

A few questions:

Question Is the bearing surface in the housing lead?

Question Is it lubricated or run dry?

Question What would you estimate the maximum possible temperature the lead ball could withstand, before danger of creeping out of shape?

Question Do you mean electroplated hard chromium instead of spray coated chrome?

Question Do you think chrome coating is failing due lack of support from lead substrate?

Gordon, thanks for your Reply,
Answer to your questions as follows:
1. There is no bearing surface in the lead housing
2. Dry lubricated, on the larger spheres air is forced around the ball help cussion the weight.
3. This would be a guess, lead melts at 328c i would say 150c
4. Having talked to our supplier it is a spray process using stainless steel not chrome as i mentuioned before, they spray on a thickness of 4mm the ball is then machined down to 2mm thickness which is when the cracking occurs.
5. This could well be the problem with machining to such a small tolerance, a lot of heat is generated on the tool tip when machining stainless which would then cause problems with the immediated substrate.

I hope these answers help, it is quite an interesting problem

Regards
Kevin.
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09-26-2006, 01:38 PM,
#4
RE: Coating of lead spheres
Hi Kevin

Sorry, a few more questions:

Question Which thermal spray process is used?

Question What sort of tolerances are achieved on the thickness of the as sprayed coating? Is it sprayed by hand or robotically?

Question Could you gives more detail of the coating material? Reason being most stainless steels would not be capable of anywhere near 4 mm thickness, except for the hard 13Cr steel types.

Question Can grinding be used to finish coating instead of single point tool?

The as sprayed coating thickness sounds very excessive and assume this is because of poor control of tolerances and needing 2 mm machining allowance to finish true.

If the coating is a 13Cr steel type, this will be pretty hard and around the limit for single point turning and quite torturous. Grinding would be the normal recommended finishing method.

My question on temperature, was not out of concern for the thermal spray process (although very important). Considering PTFE (Teflon) type coatings, which would require curing at or above the melting point of lead, but I believe there are some other non-stick polymer types that can be cure at lower temperatures. Initial thoughts, were for a relatively thin thermal spray coating/polymer combination coating which would not require any machining, but not sure if this would provide the size tolerances you may require.

Your coating may in fact be OK for this purpose if you can sort out the processing problems. I think its important to understand the problems your getting with this coating, before we start suggesting alternative coatings ("jumping out of the frying pan into the fire").
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09-27-2006, 07:56 AM,
#5
RE: Coating of lead spheres
Hi Headland!

Your problem is very interesting. I have some experiences with HVOF ball coating and grinding (2-40?? OD).
I have some questions:
1) Which outside diameter has your Tong Ball?
2) Which max. thickness of coating may be?
3) Coul?d you send sketch or drawing of this ball?

Other process - only an idea: you can produce a shell roof (from stainless steel-like casting part), than flow the melted lead into the shell and than drill the hole in lead centre.

Vladimir

Headland Wrote:We manufacture equipment for the nuclear industry, one item being a Tong Ball which is a lead sphere through which passes a tong grab, the ball is mounted in a lead shield housing allowing the operator to gimble the tong anywhere within the containment. At present the lead ball is manufactured and spray coated with chrome to reduce wear in the gimble housing, this is prone to cracking and the operation has become very expensive. Is there another coating such as a form of ceramic or teflon which can be sprayed on a spherical lead surface with an even coat to reduce the final machining and also give the required durability.
Reply
09-27-2006, 01:53 PM,
#6
RE: Coating of lead spheres
Gordon Wrote:Hi Kevin

Sorry, a few more questions:

Question Which thermal spray process is used?

Question What sort of tolerances are achieved on the thickness of the as sprayed coating? Is it sprayed by hand or robotically?

Question Could you gives more detail of the coating material? Reason being most stainless steels would not be capable of anywhere near 4 mm thickness, except for the hard 13Cr steel types.

Question Can grinding be used to finish coating instead of single point tool?

The as sprayed coating thickness sounds very excessive and assume this is because of poor control of tolerances and needing 2 mm machining allowance to finish true.

If the coating is a 13Cr steel type, this will be pretty hard and around the limit for single point turning and quite torturous. Grinding would be the normal recommended finishing method.

My question on temperature, was not out of concern for the thermal spray process (although very important). Considering PTFE (Teflon) type coatings, which would require curing at or above the melting point of lead, but I believe there are some other non-stick polymer types that can be cure at lower temperatures. Initial thoughts, were for a relatively thin thermal spray coating/polymer combination coating which would not require any machining, but not sure if this would provide the size tolerances you may require.

Your coating may in fact be OK for this purpose if you can sort out the processing problems. I think its important to understand the problems your getting with this coating, before we start suggesting alternative coatings ("jumping out of the frying pan into the fire").

Hi Gordon,
regards your questions:
1. Im affraid i do not know as our supplier uses another company to do the spraying.
2. Unsure of tolerances, our supplier tells me that they receive the ball at approx 4mm thk and at present it is sprayed by hand but the company is looking into the use of robots.
3. Sorry no info on material
4. Can't see a problem with grinding, infact the surface finish would be better.

I have a photo of the damaged spheres which are 140mm dia,do you know if i can attach to this e mail?

Regards
Kevin.
Reply
09-28-2006, 03:00 PM,
#7
RE: Coating of lead spheres
Vladimir Wrote:Hi Headland!

Your problem is very interesting. I have some experiences with HVOF ball coating and grinding (2-40?? OD).
I have some questions:
1) Which outside diameter has your Tong Ball?
2) Which max. thickness of coating may be?
3) Coul?d you send sketch or drawing of this ball?

Other process - only an idea: you can produce a shell roof (from stainless steel-like casting part), than flow the melted lead into the shell and than drill the hole in lead centre.

Vladimir

Headland Wrote:We manufacture equipment for the nuclear industry, one item being a Tong Ball which is a lead sphere through which passes a tong grab, the ball is mounted in a lead shield housing allowing the operator to gimble the tong anywhere within the containment. At present the lead ball is manufactured and spray coated with chrome to reduce wear in the gimble housing, this is prone to cracking and the operation has become very expensive. Is there another coating such as a form of ceramic or teflon which can be sprayed on a spherical lead surface with an even coat to reduce the final machining and also give the required durability.
Hi Vladimir
Answers to your questions
1. 140mm OD
2. Sprayed on to 4mm machine turned to 2mm
3. Having trouble attaching photos or sketches to this e mail

Hope this helps
Regards
Kevin.
Reply
09-29-2006, 08:19 AM,
#8
RE: Coating of lead spheres
Hi Kevin
With reference to Gordons point about Teflon coatings - there are many dry lubrication coating systems that can be applied at temperatures as low as 100 deg C. These contain either PTFE or other lubricating solids (such as moly disulphide, graphite etc). These systems could be applicable to a lead substrate either alone or in combination with a thermal spray base as suggested by Gordon.

Regards
Gary
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09-29-2006, 10:15 AM,
#9
RE: Coating of lead spheres
polysol Wrote:Hi Kevin
With reference to Gordons point about Teflon coatings - there are many dry lubrication coating systems that can be applied at temperatures as low as 100 deg C. These contain either PTFE or other lubricating solids (such as moly disulphide, graphite etc). These systems could be applicable to a lead substrate either alone or in combination with a thermal spray base as suggested by Gordon.

Regards
Gary

Many thanks for your reply, the coating systems you have mentioned look favaourable do you have any info you can send me, perhaps a company address.
Regards
Kevin
Reply
10-04-2006, 02:20 PM,
#10
RE: Coating of lead spheres
Kevin
Company details can be found on website www.polymercoatingsolutions.co.uk
Regards
Gary
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10-04-2006, 05:07 PM,
#11
RE: Coating of lead spheres
Alphatek Hyperformance Coatings Ltd
Contact: Steve Greenwood
Tel: 01706 821021

Thermal spray and polymer coatings and combination coatings.
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10-09-2006, 02:32 PM,
#12
RE: Coating of lead spheres
Headland Wrote:3. Having trouble attaching photos or sketches to this e mail

This thread may help:

Image/photo in posts
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