GB2130697A

GB2130697A - Salt quenching bath

Info

Publication number: GB2130697A
Application number: GB08329032A
Authority: GB
Inventors: Edward John Bloomfield; Harry Douglas Hendrick
Original assignee: HENDRICK IND EQUIPMENT Ltd
Current assignee: HENDRICK IND EQUIPMENT Ltd
Priority date: 1982-11-01
Filing date: 1983-10-31
Publication date: 1984-06-06
Also published as: GB8329032D0

Abstract

A salt quenching bath has walls (1-5) of corrugated structure to provide enhanced cooling and includes a dam (6) and weir (7) between which is defined a cooling channel (8). Molten salt is circulated from a quenching region (11) through the cooling channel (8) and to a filtering region (12). <IMAGE>

Description

SPECIFICATION Salt quenching bath The invention relates to a salt quenching bath for use in the quenching of heat-treated articles.

Heat-treatment of metal articles usually requires quenching under controlled conditions from a high temperature to a lower temperature.

Typically, for example, an article may have been treated by immersion in a molten-salt austenitizing bath and subsequenching is carried out by immersion in a quenching tank containing molten salt. In the quenching operation deposits from the article are carried away by the circulating salt and they must be efficiently filtered.

It is necessary to provide controlled heat extraction from the salt and also to provide insulation to allow reasonable working conditions in the neighbourhood of the bath.

The present invention seeks to provide an improved bath which is compact since it provides an efficiently large quenching and filtering area for its size; is well insulated, strong and light and effectively cooled with the minimum of water cooling.

According to one aspect of the invention there is provided a salt quenching bath with a body fabricated with a ribbed structure which defines longitudinal air channels and cooling fins whereby cooling air may circulate naturally or by being blown. Usually it will be necessary to provide an outer layer of insulation over the ribbed structure.

A removable capping may be provided to block off the cooling channels during pre-heating.

According to another aspect of the invention there is provided a salt quenching bath of essentially rectangular cross-section divided substantially midway by a vertical dam and weir arrangement, the dam and weir being separated by a cooling channel which includes cooling coils which carry cooling water, inlet to the cooling channel being over the weir from a quenching region and outlet being at a lower point into a filtering region, molten salt being recircuiated by pumps which pump the salt from the filtering region back to the base of the quenching region.

Preferably the filtering region includes a removable filter deposits basket which has a solid base for the collection of deposits and a mesh outlet face for filtration of the salt. Preferably the basket itself is shaped so as to direct the salt in its recirculation.

The invention will further be described with reference to the accompanying drawings, of which: Figure 1 is a vertical cross-section of a quenching bath in accordance with the invention; Figure 2 is a scrap cross-section of part of the wall of the bath of Figure 1; and Figure 3 is a plan view of the bath.

Referring to the drawings, the quenching bath is a rectangular unit having walls 1 constituted by a hollow shell 2 with an internal structure given by a metal corrugated ribbing 3 (Figure 2). The ribbing serves as a strengthening arrangement as well as providing longitudinal air channels and cooling fins, the cooling fins being constituted by the metal corrugations which are in thermal contact with the bath. The channels 4 defined by the corrugations are vertical and carry cooling air which extract heat from the bath by convection (although fans may be provided for forced cooling). An outer layer 5 of insulation is also provided.

The bath is divided centrally by a vertical dam and weir arrangement comprising a dam 6 and a weir 7. The space defined between the dam and the weir is a cooling channel 8 which includes coils of pipe 9 which carry cooling water.

The bath is filled with molten salt 10 which recirculates between a quench region 11 and a filter region 1 2. Circulation is effected by a pair of propellors 1 3 mounted on long shafts 14, the bearings being ceramic and salt-lubricated, driven by a single electric motor 1 5.

Salt enters the cooling channel over the weir 7, is cooled, and exits to the filter region 1 2 from the lower end 1 6 of channel 8. The filter region contains a removable filter/deposits basket 1 7 which has a solid-sided collection basket portion 18 and a mesh face 1 9 and sides for filtering the salt of deposits released by the articles being quenched. Guide vanes 20, as well as the shape of the basket portion 18, conduct the molten salt in the path indicated by the arrows whereby it is returned to the quench region.

In order to heat the molten salt initially to the required quench temperature there are provided electric heaters 21. During heating, in order to minimise heat loss, caps 22 are placed over the tops of the cooling channels 4.

The arrangement illustrated provides full-width quenching, laminarflow and deposits collection; a large area filter; high-powered circulation; quick and efficient heat-up and efficient and economical cooling.

The invention is not limited to the features of the embodiment described with reference to the drawings.

In particular, three preferred features which are not illustrated are: (a) a corrosion-retarding strip seal welded to the inside of the tank at the salt-air level; (b) couplings in the drive shafts for the circulating propellors which include a heat dissipating rotor with blades to throw off heat and a heat-resistant low-conductive centre; and (c) the provision of external heating by electrically resistive tiles which clad selected parts of the bath.

1. A salt quenching bath with a body fabricated with a ribbed structure which defines longitudinal air channels and cooling fins whereby cooling air may circulate naturally or by being blown.

2. A salt quenching bath as claimed in claim 1 wherein there is provided an outer layer of insulation over the ribbed structure.

3. A salt quenching bath as claimed in either of the preceding claims wherein removable capping

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Salt quenching bath The invention relates to a salt quenching bath for use in the quenching of heat-treated articles. Heat-treatment of metal articles usually requires quenching under controlled conditions from a high temperature to a lower temperature. Typically, for example, an article may have been treated by immersion in a molten-salt austenitizing bath and subsequenching is carried out by immersion in a quenching tank containing molten salt. In the quenching operation deposits from the article are carried away by the circulating salt and they must be efficiently filtered. It is necessary to provide controlled heat extraction from the salt and also to provide insulation to allow reasonable working conditions in the neighbourhood of the bath. The present invention seeks to provide an improved bath which is compact since it provides an efficiently large quenching and filtering area for its size; is well insulated, strong and light and effectively cooled with the minimum of water cooling. According to one aspect of the invention there is provided a salt quenching bath with a body fabricated with a ribbed structure which defines longitudinal air channels and cooling fins whereby cooling air may circulate naturally or by being blown. Usually it will be necessary to provide an outer layer of insulation over the ribbed structure. A removable capping may be provided to block off the cooling channels during pre-heating. According to another aspect of the invention there is provided a salt quenching bath of essentially rectangular cross-section divided substantially midway by a vertical dam and weir arrangement, the dam and weir being separated by a cooling channel which includes cooling coils which carry cooling water, inlet to the cooling channel being over the weir from a quenching region and outlet being at a lower point into a filtering region, molten salt being recircuiated by pumps which pump the salt from the filtering region back to the base of the quenching region. Preferably the filtering region includes a removable filter deposits basket which has a solid base for the collection of deposits and a mesh outlet face for filtration of the salt. Preferably the basket itself is shaped so as to direct the salt in its recirculation. The invention will further be described with reference to the accompanying drawings, of which: Figure 1 is a vertical cross-section of a quenching bath in accordance with the invention; Figure 2 is a scrap cross-section of part of the wall of the bath of Figure 1; and Figure 3 is a plan view of the bath. Referring to the drawings, the quenching bath is a rectangular unit having walls 1 constituted by a hollow shell 2 with an internal structure given by a metal corrugated ribbing 3 (Figure 2). The ribbing serves as a strengthening arrangement as well as providing longitudinal air channels and cooling fins, the cooling fins being constituted by the metal corrugations which are in thermal contact with the bath. The channels 4 defined by the corrugations are vertical and carry cooling air which extract heat from the bath by convection (although fans may be provided for forced cooling). An outer layer 5 of insulation is also provided. The bath is divided centrally by a vertical dam and weir arrangement comprising a dam 6 and a weir 7. The space defined between the dam and the weir is a cooling channel 8 which includes coils of pipe 9 which carry cooling water. The bath is filled with molten salt 10 which recirculates between a quench region 11 and a filter region 1 2. Circulation is effected by a pair of propellors 1 3 mounted on long shafts 14, the bearings being ceramic and salt-lubricated, driven by a single electric motor 1 5. Salt enters the cooling channel over the weir 7, is cooled, and exits to the filter region 1 2 from the lower end 1 6 of channel 8. The filter region contains a removable filter/deposits basket 1 7 which has a solid-sided collection basket portion 18 and a mesh face 1 9 and sides for filtering the salt of deposits released by the articles being quenched. Guide vanes 20, as well as the shape of the basket portion 18, conduct the molten salt in the path indicated by the arrows whereby it is returned to the quench region. In order to heat the molten salt initially to the required quench temperature there are provided electric heaters 21. During heating, in order to minimise heat loss, caps 22 are placed over the tops of the cooling channels 4. The arrangement illustrated provides full-width quenching, laminarflow and deposits collection; a large area filter; high-powered circulation; quick and efficient heat-up and efficient and economical cooling. The invention is not limited to the features of the embodiment described with reference to the drawings. In particular, three preferred features which are not illustrated are: (a) a corrosion-retarding strip seal welded to the inside of the tank at the salt-air level; (b) couplings in the drive shafts for the circulating propellors which include a heat dissipating rotor with blades to throw off heat and a heat-resistant low-conductive centre; and (c) the provision of external heating by electrically resistive tiles which clad selected parts of the bath. CLAIMS

3. A salt quenching bath as claimed in either of the preceding claims wherein removable capping is provided to block off the cooling channels during pre-heating.

4. A salt quenching bath of essentially rectangular cross-section divided substantially mid-way be a vertical dam and weir arrangement, the dam and weir being separated by a cooling channel which includes cooling coils which carry cooling water, inlet to the cooling channels being over the weir from a quenching region and outlet being at a lower point into a filtering region, molten salt being recirculated by pumps which pump the salt from the filtering region back to the base of the quenching region.

5. A salt quenching bath as claimed in claim 4 wherein the filtering region includes a removable filter deposits basket which has a solid base for the collection of deposits and a mesh outlet face for filtration of the salt.

6. A salt quenching bath as claimed in claim 4 or claim 5 wherein the basket is shaped so as to direct the salt in its recirculation.

7. A salt quenching bath as claimed in any of claims 4 to 6 which is fabricated with a ribbed structure which defines longitudinal air channels and cooling fins whereby cooling air may circulate naturally or by being blown.

8. A salt quenching bath as claimed in claim 7 wherein there is provided an outer layer of insulation over the ribbed structure.

9. A salt quenching bath as claimed in claim 7 of claim 8 wherein a removable capping is provided to block off the cooling channels during pre-heating.

10. A salt quenching bath substantially as hereinbefore described with reference to the accompanying drawings.